Fatigue testing machine



Ap 7, 1954 B. J. LAZAN FATIGUE TESTING MACHINE 2 Sheets-Sheet 1 Filed Feb. 14, 1951 INVENTOR. BENJAMIN J. LAZAN HTWRNEYS April 27, 1954 I B. J. LAZAN 2,676,486

FATIGUE TESTING MACHINE Filed Feb. 14, 1951 2 Sheets-Sheet 2 IN VEN TOR. BENJAMIN J. Lnz/a/v FIG .6 Q BY 6 Patented Apr. 27, 1954 FATIGUE TESTHNG MACHINE Benjamin J. Lazan, Minneapolis, Minn, assignor to the United States of America as represented by the Secretary of the Navy Appiication February 14, 1951, Serial No. 210,853

15 Claims.

The invention ibcd herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention pertains to the art of testing materials, and it is embodied in a machine for determining damping capacity, dymodulus of elasticity and fatigue properties of materials.

Apparatus or" the p'esent invention operates to apply flexure stress to an elongated specimen of the material, fiexure stresses being repeated at prcdeter-..ined time intervals and often as is required for a given test. Repeated fissure stresses are applied by rotating specimen on its lengthy ise axis.

The specimen is provided with a contour which symmetrical around its lengthwise axis, i. enters of gravity of increment transverse cross-sections lie in a straight line coincident with the geometrical. longitudinal axis of the specimen. The simplest form of specimen is cylindrical with the axis of the cylinder being coincident with the lengthwise center-dine of mass. The specimen of the disclosure, as it wtually used in practice of the invention, is to the conventional test specimen for tens le specimen is H bent and held in bent condition so that the axis of the specimen is defiected away from the axis of the cylinder. By rotating the bent specimen on its axis, it is repeatedly flexed diametrically, the resultant repeated fiexure stresses being applied on successive radii circumferentially. Successive flc-Xure stresses are applied progressively around the specimen reversely of its direction of rotation.

Apparatus of the invention is embodied in a machine which comprises a rotatable spindle. The specimen is secured at its one end to the spindle coaxially therewith. At its other end, the specimen is secured to a coaxial shaft, the free end of which remote from the specimen is held displaced in a static direction away from the axis of the spindle extended.

The free end of the shaft preferably is dis placed out of line with the axis of the spindle by a weight, which is attached to the shaft a predetermined distance along its length away from the end of the specimen. The weight applies a cantilever load that bends the specimen. The spindle, and also the shaft that carrie the weight, are constructed strong enough to not bend appreciably under the load of the weight,

and bonding is therefore confined to the specimen.

The spindle is carried by an adjustable mount to vary the angle of inclination of the axis of the spindle. The horizontal moment arm of the weight is thereby varied to adjust the cantilever load on the specimen and thus vary the magnitude of nexure of the specimen accordin ly.

Curvature of the axis of the specimen cylinder is a measure of the magnitude of flexure of the specimen, and the measurement is made by measuring the displacement of the fre end of the sh .t. A. central target at the free end of the shaft is observed through a microscope which is mounted to View the target endwise of tl e specimen. The microscope mount includes Laverse in the direction of the ordinate corresponding with the specimen being bent by dead-weight. An additional traverse of the microscope in the lateral or transverse direction of the abscissa determines lateral or transverse displacement of the target due to rotation of the specimen on its axis.

A vibration damper is provided to steady the position of the target, and thereby enables its displacement to be read more easily and accurately. The vibration damper comprises a pair of plates bearing against each other face-toiace, and a him of oil between the plates reduces on to hold the error by friction of target displacement negligibly low. Therefore, any error of target displacement reading that is caused by friction drag is so low that it does not aiiect the accuracy of test findings.

For a fuller understanding of the principles of the invention, and for details of one practical embodiment thereof, attention is directed to the accompanying drawings. In the drawings 1 is a side elevation of a machine embodying the invention,

Fig. 2 is a fragmentary side elevation, partially in cross-section, of certain components of the machine of Fig. 1, illustrating a second position of machine operation,

Fig. 3 is a cross-sectional plan, taken on line t-3 of Fig. 2,

Fig. 4 is a cross sectional elevation, taken on line di of Fig. 3,

Fig. 5 is a detailed end view of the target as viewed from the position of the microscope,

Fig. 6 is a fragmentary cross-sectional elevation, taken on line t-8 of Fig. 5,

Fig. '7 is a schematic side elevation, illustrating principles of operation of the invention, and

Fig. 8 is a diagrammatic view, illustrating 3 measurements that are taken to determine properties of materials by means of the machine of Fig. 1.

The machine of the disclosure comprises a rigid foundation or base ll, Fig. l, which preferably is disposed horizontally, and which embodies the horizontal pivot I2.

An upright table or platen i5 is supported by the base II to swing on the pivot I2. The brace I6 also swings on a horizontal pivot ll of the base ll, pivots l2 and i! being parallel. The pivot I! is a connection between the base H and the brace H5 at its one end, and a similar pivotal connection 18 between the platen l5 and the brace It at its other end is parallel with pivots I? and I2.

The described structure enables the platen It to be positioned at various angles of inclination with reference to horizontal, and traversing mechanism is provided to adjust the position of inclination of the platen i5. The traversing mechanism comprises the lead or traverse screw I9 carried by the platen l5 and directed lengthwise thereof at right angles to the pivot 12. Traverse screw [3 is threaded through the shank of pivot I8 transversely of its axis as seen in Fig. 3, and the pivot It! therefore constitutes a traversing carriage or nut that travels along screw Hi. The handle or hand wheel 20 serves for manual rotation of traverse screw l9 to drive the nut l8 and thereby adjust the platen IE to the desired angle of inclination.

The spindle 22 is rotatable in the journal 23, which is secured to the platen by means of the brackets 24 that hold the axis of the spindle parallel to the platen 15. In the position illustrated in Fig. 1, the axis of the spindle 22 is vertical. Rotation of the hand wheel to traverse the nut I8 upwardly along the screw l 9 causes the axis of spindle 22 to tilt with base l5 out of vertical position shown in Fig. 1, and into an inclined position, for example, into the position illustrated in Fig. 2.

The motor is mounted on the journal 23 by means of support brackets 26, and includes any suitable revolution counter 21. The spindle 22 is driven from the motor 25 by means of the belt 28.

The specimen is an elongated piece or the material to be tested and is contoured symmetrically around its longitudinal axis. closure, and in accordance with common and preferred practice, the specimen is similar to conventional tensile-test specimens and comprises a cylinder of predetermined length. At its one end, the specimen 30 is secured to the adaptor 3| which fits the attachment 32 at the end of spindle 22, and by means of which the specimen 33 is secured at its one end to the spindle 22 coaxially therewith.

The shaft 33 is secured to the other end of the specimen 3U coaxially therewith by means of the adaptor 34. The shaft 33 is tapered as shown, and the weight 35 has a tapered bore Which fits the shaft 33. The weight 35 is circular, and is mounted coaxial with shaft 33. The nut 35 holds the weight 35 secured to the shaft 33 for rotation therewith, and the weight 35 is thus positioned along the shaft a predetermined distance away from the specimen 30.

When the base [5 is tilted by the handle 23 being rotated, for example, from the vertical position of Fig. 1 to the inclined position of Fig. 2, the axis of the spindle, 22, and the common axis of spindle 22, shaft 33 and specimen 33, is also inclined. The weight 35 thus comprises a canti- In the dislever load that tends to deflect the common axis of spindle 22, shaft 33 and specimen 30 away from the angle of inclination determined by the angle of adjustment of platen l5. The spindle 22, as also the shaft 33, are each constructed stronger than specimen 30 so that they do not bend appreciably under the load of Weight 35. The cylindrical specimen 30 is small enough to bend under the load of weight 35, and bending along the continuous axis of spindle 22, specimen 3% and shaft 33 is confined virtually entirely within the cylindrical length of specimen 3!]. The shaft 33 is tapered as shown to dimensions which diminish along the shaft progressively away from its point of suspension, this being in accordance with established principles of cantilever construction. For the practical purpose of tests made by the machine of the disclosure, the total deflection of the common axis of spindle 22, specimen 30 and shaft 33 is concentrated in the specimen, and the specimen 30 is bent to curved condition under the load of the weight 35.

Figs. '7 and 8 serv to illustrate schematically the deflection by the weight 35, the illustration being exaggerated to demonstrate the principles more clearly. It will be noted that, because the specimen 30 has become bent under the deadweight load of weight 35, the tip 40 of shaft 33 has become displaced downwardly from the axis of spindle 22 extended. Viewed lengthwise, the

' axis of spindle 22 is at a in Fig. 8, and tip 40 oocupies the position a when the base l5 is in vertical position of Fig. I. By the base 15 being inclined to the position of Fig. 2 or the position of Fig. 7, the point 43 has become depressed away from the spindle axis at a to position b along the ordinate ab which coincides with the vertical plane described by the curved axis of specimen 3%. The distance wb that the point ifl is depressed depends upon the horizontal moment arm of weight 35, i. e., the horizontal distance between the center of gravity of weight 35 and the lengthwise center of the cylinder of specimen 30.

The shaft 33 at its end All, Figs. 1 and 2, is formed tubular as illustrated in detail in Figs, 5 and 6. Each of the set screws 42 is threaded radially through the wall of the tubular end 4!, and they are disposed in coaxial sets that are diametrically opposite each other and thus serve to clamp the tip or target 43 in position along the geometric axis of the shaft 33.

The microscope 44 is supported on the base i5 by means of the mount 45, which comprises the carriage 45 on which the pillar 47 is secured to project away from the base [5. The microscope 3 is attached to the pillar 41 in any suitable manner for traverse lengthwise thereof by rotation of the handle or handwheel :28, the scale 49 being included to indicate the distance of traverse. l-landwheel 50 is rotatable to traverse the carriage 55 in a direction at right angles to the axis of traverse 48, and a scale is provided for the traverse 50 that indicates the distance of its travel. Traverse by handle 48 is in the direction of an ordinate, and the traverse of handle 53, which is perpendicular to the traverse of handle 48, is along an abscissa.

The microscope 44 and its mount may be individually old in prior art instruments of various kinds, and requires no detailed disclosure herein. It is sufficient to know that the microscope M is supported by the pillar 41 for viewing through the eye-piece 5| in the direction of the axis of spindle 22 or in a line that is parallel thereto. The microscope 44 includes the knob 52 to focus 5 the lenses of the microscope, and the knob 53 to focus the microscope to the object, these adjustments being commonly present in microscope structures.

The microscope M is sighted on the target Mi. When the base it is tilted by adjustment of the handwheel 2c, the target ts will move under the load of the weight 35 along a line that constitutes an ordinate, for example from position a to position in Fig. This movement may be measured by the microscope l being traversed by rotation of handle to track the target cc, and the scale as is read to determine the magnitude of displacement of target it under deadweight load of the weight 35.

When the motor 25 is operated to drive the spindle 22, this rotation produces additional deflection of the target ll] laterally, lateral deflection being to the left, for example to position in Fig. 8, when the spindle 22 is rotated clockwise, and lateral deflection being to the right when spindle 22 is rotated counter-clockwise, to position d, for example. The microscope at is moved to the left or right by the traverse 50 to track the laterally, and a suitable scale determines the distance of lateral displacement.

While the motor 25 drives the spindle 22, the target iii remains stationary in a predetermined position away from the point a in Fig. 8, at point (1 for example, the magnitude of displacement of target dd for a specimen of given material being determined by the angle of inclination of the base is, and by the speed of rotation of the spindle which may be determined by any suitable tachometer. This operation subjects the specimen St to successive bends, the magnitude of bends being proportionate to the diameter of radius a-d, Fig. 8. The specimen 3% will be bent successively circumferentially on all of its radii, and this continues repeatedly in the direction reverse of rotation at the rate determined by the P. M. of the spindle 22.

The shaft projects through the aperture 55 of the bracket 5t which is supported on the base it as illustrated in Figs. 1 and 2. The pushbutton Ell is mounted at the base of the aperture in the path of the shaft 33 under load of the weight and the micro-switch 58 is operated when push-button til is depressed to thereby stop motor by any suitable electrical connection therewith. The usual practice is to continue a test a particular material of specimen so until failure. When the material fails, and rupture takes place, the Weight 35 falls, and the shaft falls with it and strikes the push-button 5i to stop motor 25. The motor 25 is thus automatically stopped by failure of specimen 3E and the amount of fiexural stress that produced failure of the specimen is determined by reading the revolution counter 21.

There is a tendency of the target at to vibrate at its stationary position c or d, Fig. 8, during a test run. The center of mass of circular weight is coincident with the center of shaft 33, but this is only theoretically so. There is suflicient deviations from precise homogeneity of the material of weight 35, and perhaps slight deviation from accurate machining of parts, which throws the rotating mass off center sufficiently to cause the target it to vibrate as it is observed through microscope i i. A novel damping device 60, Figs. l and 2, and illustrated in detail in Figs. 3 and 4, operates to hold the target steady and to eliminate its vibration, and the target All is thereby held stationary to enable its position to be read iii) 6. easily and accurately by means of the microscope 44.

The clamping device 60 comprises a stationary member 6! in the form of a disc with a concentrio hole 62, the hole being large enough to contain the end ti of shaft 33 without touching for any position of displacement of target til. For holding the stationary member 6i suspended in fixed position in space, the bar 53 is secured thereto and includes the clamp lit by means of which the disc is attached to the post 65, which projects away from I5 and is secured thereto along its edge at 66. The position of the stationary member ill with reference to the shaftend ll is adjustable by means of the clamp 6d, the adjustment serving to locate the end ll of shaft 33 within the hole 62 at or near the center thereof when the platen i5 is in vertical position of Fig. 1.

The floating sheath El, also in the form of a disc, is larger than the hole 62 and comprises the concentric bushing til. The end 4! of shaft 33 is cylindrical and constitutes a bearing for which the bushing 68 is a journal. The bore 69 of bushing 5% is formed arcuate in the lengthwise direction to adjust itself to the bearing 1! when the axis of shaft 33 is tilted out of coaxial alignment with spindle 22 under load of the weight The disc ill rests on the disc 6i, with the frat bottom surface of disc ti bearing against the flat top surface of disc 6! in frictional engagernent therewith.

A film of oil is provided between the opposed surfaces of the discs 8? and SE for uniform and smooth frictional drag to steady the position of the target ed. The oil film between the discs 6'! and ti provides lubrication which reduces the frictional error of the vibration damping device lit negligibly low. Several circular concentric grooves it, and the radial groove ii that connects the circular grooves, are filled with lubricating oil, and provide a sufficient supply of oil to maintain friction values constant during a test.

The hereinbefore presented description of the machine structure and its operation enables persons skilled in the art to understand the usefulness of the apparatus for determining fatigue properties of materials, damping capacity and dynamic modulus of elasticity without the need of further elaboration.

The machine shown in the drawing is one practical embodiment of the invention, which is not limited to the disclosed structure. The scope of the invention is determined by the accompanying claims.

I claim:

1. In a machine for testing materials, a spindle attached to one end of a specimen of the material coaxially with its longitudinal mechanism to bend the specimen and displace the other end of the specimen out of coaxial alignment with the spindle and comprising a shaft projecting coaxially of the specimen from the end of the specimen remote from the spindle, a weight of predetermined mass carried by the shaft a predetermined distance along the shaft away from its attachment to the specimen, the center of mass of the weight being coincident with the axis of the shaft, a motor to drive the spindle and rotate the specimen on its longitudinal axis, and apparatus to measure displacement out of coaxial alignment with the spindle of the end of the specimen remote from the spindle.

weight being circular and rigidly secured to the shaft concentrically therewith.

3. In a machine as defined in claim 1, the apparatus for measuring displacement of the end of the specimen remote from the spindle comprising a microscope, and a mount for the microscope holding it for viewing in the direction of the axis of the spindle towards the displaced end of the shaft.

4. In a machine as defined in claim 3, the microscope mount comprising a traverse mechanism for each of two dimension displacement of the microscope and a scale for each traverse mechanism to indicate corresponding linear displacement of the microscope, one traverse mechanism paralleling the ordinate corresponding with displacement of the shaft by dead-weight load of the weight, and the other traverse mechanism paralleling an abscissa corresponding with lateral displacement of the shaft by rotation of the spindle.

5. In a machine as defined in claim 4, a target at the end of the shaft concentrically therewith, and an adjustment for concentricity of the target.

6. In a machine as defined in claim 4, a device for damping vibration of the free end of the shaft remote from the specimen.

7. In a machine as defined in claim 6, the vibration damping device comprising a bearing near the free end of the shaft, the bearing comprising a stationary member with a top surface that is fiat, a sheath comprising a journal for the bearing, the sheath resting on the stationary member and comprising a flat bottom surface bearing against the fiat top surface of the stationary member in frictional engagement therewith.

8. In a machine as defined in claim 7, the stationary member comprising a plate with a hole positioned around the bearing of the shaft out of contact therewith, the plate comprising a flat top surface, the sheath comprising a disc supporting the journal concentrically, the disc being larger than the hole of the plate and resting loosely on the plate, and the disc of the sheath comprising a flat bottom surface bearing on the flat surface of the plate in frictional engagement therewith.

9. In a machine as defined in claim 8, an adjustment for the stationary member to locate the journal in accordance with the position of the free end of the shaft when the machine is operating or not operating.

10. In a machine as defined in claim 8, grooves in the top surface of the plate to contain a fluid lubricant.

11. In a machine as defined in claim 10, the grooves including a plurality of circular grooves concentric with the hole of the plate and with each other and a radial groove connecting the circular grooves.

12. In a machine as defined in claim 1, a mount for the spindle comprising adjusting mechanism to vary the angle of inclination of the spindle with reference to the horizontal.

13. In a machine for testing materials, a base, a platen carried by the base and comprising a horizontal pivot to swing the platen on the base, adjusting mechanism to vary the inclination of the platen to various angles between vertical and horizontal, a spindle supported by the platen to rotate on an angle parallel therewith, an attachment at one end of the spindle to engage a specimen of the material at its one end and hold the specimen coaxially with the spindle, a motor to drive the spindle and rotate the specimen on its longitudinal axis, mechanism comprising a rigid shaft secured to the end of the specimen remote from the spindle coaxially of the specimen, the end of the shaft remote from the specimen being free and comprising a concentric weight carried by the shaft, and apparatus for measuring displacement of the free end of the shaft when the specimen is bent by the platen being adjusted to a position that is inclined out of vertical position.

14. In a machine as defined in claim 13, the apparatus for measuring displacement comprising a microscope, and a mount for supporting the microscope on the platen in position for viewing the displaced end of the shaft in the direction of the axis of the spindle.

15. In a machine as defined in claim 13, the adjusting mechanism for the platen comprising a brace for the platen connected pivotally at its respective opposite ends to the base and to the platen, the pivotal connection between the brace and the platen comprising a nut, the platen comprising a traverse screw threaded through the nut and directed lengthwise of the platen, and a handle to rotate the traverse screw to vary the angle of inclination of the platen with reference to the horizontal.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,193,686 Heisler Aug. 8, 1916 1,507,412 Bryson Sept. 2, 1924 1,667,401 Stockmeyer Apr. 24, 1928 2,170,640 Kenyon Aug. 22, 1939 2,235,622 Ray Mar. 18, 1941 2,435,772 Clarke Feb. 10, 1948 2,436,096 Chubb Feb. 17, 1948 2,466,327 Rieber Apr. 5, 1949 2,514,140 O'Connor July 4, 1950 2,614,415 Kepes Oct. 21, 1952 FOREIGN PATENTS Number Country Date 721,553 France Dec. 22, 1931 530,418 Great Britain Dec. 11, 1940 598,510 Great Britain Feb. 19, 1948 

